The invention concerns a valve train of an internal combustion engine, said valve train comprising a tappet push rod, a tappet, a hydraulic lash adjuster and an uncoupling device for selectively uncoupling the valve train from a lifting motion of a cam, said tappet push rod comprising on a first end, the tappet and on a second end, a contact surface for activating a rocker arm, which tappet can be loaded by the cam and extends in a reception of the internal combustion engine, the lash adjuster and the uncoupling device being arranged in a region of said first and second ends of the tappet push rod.
In a generic valve train of the pre-cited type disclosed in DE 198 44 202, the tappet comprises both the lash adjuster and the uncoupling device. Due to this complex configuration, the tappet has an undesirably large mass. Moreover, the hydraulic lash adjuster has to be supplied with hydraulic medium through the tappet push rod. This relatively long supply path can lead to problems of inadequate supply of hydraulic medium to the lash adjuster, for instance, at a cold start or a re-ignition of the internal combustion engine.
It is an object of the invention to provide a valve train of the pre-cited type in which the aforesaid drawbacks are eliminated.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that only the tappet and the uncoupling device are configured together as a single component, the lash adjuster is arranged on the second end of the tappet push rod and comprises the contact surface.
This measure leads to a clear reduction of the total mass of the tappet including the uncoupling device compared to prior art devices. At the same time, a tappet is obtained that has only small overall dimensions especially in the direction of its diameter. This arrangement of the hydraulic lash adjuster, which is known per se, on the second end of the tappet push rod, enables the lash adjuster to be supplied directly with hydraulic medium without the otherwise long oil path through the tappet push rod.
It will be clear at this point to a person skilled in the art, that due to its xe2x80x9chighxe2x80x9d arrangement, the lash adjuster is completely filled with hydraulic medium at a very early point of time after the ignition of the internal combustion engine. Rattling noises and the like are therefore reduced to an extremely low level.
At the same time, due to the spatial separation of the lash adjuster from the coupling device, it is possible to use known types of lash adjusters in place of relatively complex structures that would otherwise be required.
In an advantageous configuration of the single component, it is proposed, for example, to use at least one piston as a coupling element. However, it is also conceivable to use other coupling elements like balls, wedges and other similar components.
A particularly low-friction contact of the cam on the tappet is obtained if the cam contacting surface of the tappet is configured as a roller that may be mounted on a rolling bearing.
Further features of the invention relate to an anti-rotation device of a simple configuration for preventing a rotation of the single component relative to its reception in the internal combustion engine. For this purpose, a rotation-preventing body can extend radially inward from the reception toward the outer peripheral surface of the housing of the single component. A longitudinal groove is arranged opposite this body on said outer peripheral surface. Advantageously, this antirotation device is configured as a guide bridge that is associated to a plurality of components and extends along the internal combustion engine. This bridge can comprise two opposing side walls each of which engages partially into a longitudinal groove of the housing. This guide bridge or strip can also be used as a mounting aid, not specifically represented, for the single component.
A contribution to weight reduction is obtained if the guide bridge is made of a lightweight material such as plastic.
Further propositions of the invention relate to the fixing of the lash adjuster on the second end of the tappet push rod. For example, a housing of the lash adjuster may be fixed on the tappet push rod by a simple positive and/or force-locked connection. More particularly, the housing may comprise a cylindrical extension which is plugged with the outer or inner peripheral surface of the tappet push rod. A pressure piston situated in the housing of the lash adjuster advantageously comprises, directly on its end oriented away from the tappet push rod, the contact surface for the rocker arm.
The valve train of the invention is preferably configured so that it can be completely uncoupled from the cam lift but it is also conceivable to realize partial lifts in the uncoupled state.
The total oscillating mass of the valve train can be reduced particularly when the weight of the tappet push rod is also minimized by making it, for example, as a thin-walled tube or even as a plastic tube or the like.